Method of measuring the battery level in a mobile telephone

ABSTRACT

Measuring the voltage level of a mobile telephone battery during a charging operation involves disabling the charge temporarily so that the battery rapidly enters discharge mode. The discharge mode voltage is more representative of the true battery charge level, so that the present invention can be implemented to provide a battery charge level display that is accurate even when the telephone is being charged.

This application is a continuation of U.S. patent application Ser. No.11/511,447, filed Aug. 29, 2006, which is a continuation of U.S.application Ser. No. 10/203,715, filed Mar. 31, 2003, now U.S. Pat. No.7,102,329, both of which are herein incorporated by reference in theirentirety.

BACKGROUND

1. Field of the Invention

This invention relates to a method of measuring the battery level in amobile telephone. The term ‘mobile telephone’ used in this patentspecification should be expansively construed to cover any kind ofmobile device with communications capabilities and includes radiotelephones, smart phones, communicators, and wireless informationdevices. It includes devices able to communicate using not only mobileradio such as GSX or UMTS, but also any other kind of wirelesscommunications system, such as Bluetooth.

2. Description of the Prior Art

It is desirable to monitor the battery level in a mobile telephone forvarious reasons. For example, users need to be presented with anaccurate indication of battery charge level whilst the phone is inordinary use so that the phone can be re-charged in a timely manner.Similarly, users need to know how effective charging up has been to tellif further charging is required. However, conventional battery chargelevel measurement techniques have significant problems. For example, thevoltage of a battery can be measured during charging to give anindication of the battery charge level. However, batteries typicallyapproach their maximum voltage within 10 minutes of charging, eventhough a full charge may take 60 minutes or more, so that a batterycharge level indicator just measuring battery voltage will be verymisleading. There is a pressing need for a more accurate method ofmeasuring battery levels during charging.

A mobile telephone typically presents to the user a graphical indicationof the state of the battery charge level: for example, there could be animage of a battery, divided into 4 segments. When no segments arepermanently displayed, then the battery is low. When all segments aredisplayed, the battery is full. Generally, for a given segment to bedisplayed, the voltage delivered by the battery must exceed a givenvoltage threshold. Hence, for a 4 segment display, there would be 3voltage thresholds.

Whilst a mobile telephone is in normal use (e.g., in idle mode or inactual communication), conventional battery level measurementtechniques, based upon measuring voltage levels, are more accurate.However, one complicating factor is that these voltage thresholdsconventionally differ depending on whether the telephone is in idlemode, or is in communication, or is charging. Ensuring that the correctthreshold voltage value is used in the battery level computation addscomplexity to conventional systems. Moreover, measured battery voltagesare very noisy due to the complexity of a cellular system and specificfiltering is needed to get reliable information.

BRIEF SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there isprovided a method of measuring the voltage level of a mobile telephonebattery during a charging operation comprising the steps of:

(a) applying a current source to charge the battery;

(b) temporarily causing the current from the current source to cease toenable the battery to enter a discharge mode;

(c) measuring the voltage level of the battery when in discharge mode;and

(d) re-applying current from the current source;

(e) repeating steps (b) and (c) until the measured voltage exceeds oneor more pre-determined voltage thresholds.

Hence, by disabling the charge temporarily, the battery enters dischargemode. This may be facilitated by drawing a small current equivalent tooperational drain; 100 mA is a typical figure. Typically, the charge isdisabled for a short time period in comparison to the charging period,for example approximately 1 in every 10 seconds so that overall chargingefficiency is not significantly affected. The discharge mode voltage ismore representative of the true battery charge level, so that thepresent invention can be implemented to provide a battery charge leveldisplay that is accurate even during a charging operation.

Preferably, a battery level display on the telephone indicates thecharge level of the battery in dependence on which pre-determinedvoltage threshold or thresholds has or have been exceeded. In apreferred embodiment, the battery level display can indicate 4 batterycharge levels. The above method is used to determine whether the batterycharge level should be displayed as falling within any of the first 3levels; a measurement of current charge can be taken to determine iflevel 4 has been reached.

In a second aspect, there is provided a method of measuring the voltagelevel of a mobile telephone battery during normal operation comprisingthe steps of:

-   -   (a) measuring the voltage level of the battery, the voltage        level fluctuating within an envelope of voltage values;    -   (b) filtering the measured voltage levels using a filter which        outputs a filtered voltage output which remains at a pre-defined        position in relation to the envelope of voltage values; and    -   (c) using the filtered voltage output as a measurement of the        voltage level of the battery.

By ‘normal operation’, we refer to either idle mode and/or communicationmode. Preferably, the filtered voltage output remains at or near the topof the actual voltage discharge waveform; the filter may be a one-waysliding filter which moves down very slowly but moves up very quickly.Preferably, a battery level display on the telephone indicates thecharge level of the battery, depending upon which pre-determined voltagethreshold or thresholds has or have been exceeded.

This approach can enable the same voltage thresholds to be used in bothcommunication and idle modes, compared to prior art systems whichrequired more complex arrangements which could discriminate between eachmode and apply different voltage thresholds within each mode. Further,the filtered voltage output can be used to accurately determine when thebattery is very close to being empty of charge; it is important to beable to do this since a premature detection of this state results in anunnecessary loss of operational time; conversely, if done too late,information (such as last call information and various timing data)stored in the mobile phone can be lost and the de-registration processfrom the network can be defective.

Another advantage of the filtered waveform approach is that the samevoltage thresholds may be used in all operational modes, for examplecharge, discharge, idle and communication modes. Further, no specifichardware need be supplied solely to implement this approach since it canbe performed in software.

In a third aspect, there is provided a mobile telephone adapted toperform the methods of the first and second inventive aspects definedabove.

In a fourth aspect, there is provided software programmed to perform themethods of the first and second inventive aspects defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing normal voltage discharge against time for aphone in communication mode.

FIG. 2 is a graph showing the filtered output voltage in relation to thenormal voltage discharge against time for a phone in communication mode.

FIG. 3 is a block diagram of a portion of a mobile telephone accordingto one aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Charging Mode

It is not practical to use the same voltage thresholds to estimate thebattery charge and discharge levels, since the voltage curve duringcharge is completely different from the discharge curve. In essence, thechemistry of the battery is such that its voltage during charge reachesvery quickly its maximum level after a few minutes of charge. For thisreason, you cannot use the battery voltage during charge as a reliableindication of the charge level. Also, you cannot define a separate setof thresholds for the charge level indication, as it would lead toinconsistencies between the levels applicable during charge anddischarge states.

The solution to this problem has been found by periodically disablingthe charger during charge, to return the battery to its discharge state,then measuring the voltage level and comparing it to the existingvoltage thresholds. Since the end of charge is determined by a currentmeasurement, this method is only used to determine the crossover forvoltage levels 1, 2 and 3 in an embodiment with 4 battery charge levels.

The algorithm works as follows (from empty battery):

Begin

Do ADC (Analog to Digital Conversion) measurement and calibrate;

If measurement<95% of Typical_Battery_Voltage then

-   -   we are at level 0 (battery empty),    -   do not disable charge;    -   Wait 10 seconds        Repeat until ADC measurement>95% of Typical_Battery_Voltage

Begin

Disable charger;

Do ADC (Analog to Digital Conversion) measurement;

Re-enable charger;

Pass the result to the battery display management for level comparisonwith thresholds;

Wait 5 seconds;

Repeat until MMI=level 3

Begin

Wait 10 seconds

Measure Charge Current

Repeat until Current<end of charge current thresholdSet battery display to level 4

As this method only disables the charge for approximately 1 out of every10 seconds, for approximately ⅔ of the charging period, we can assumethe charge to be nearly 95% efficient, yet accurate.

Communication Mode

A GSM communication consists of a low current consumption for most ofthe time, followed by high current bursts during radio activity. ADC(Analog to Digital Conversion) measurements are taken during a burst andothers are taken outside a burst. Moreover, the battery voltage duringcommunication is very noisy due to this bursted mode. The FIG. 1waveform is measured during communication.

Using a non-linear (“one way”) filter, the level at the top (outside aburst) can be estimated. The filter works as follows:

The filtered value T(n−1) at time (n−1) is what is used as the referencevalue.

The initial value T(0) is set before communication has begun (measuredduring initialization & then follows battery level in idle mode)

A new measurement Tmeas (n) is made at time (n):

-   -   If the new measurement Tmeas (n) is greater than the previous        value T(n−1), the filtered value at time (n) becomes the        measured value T(n)=Tmeas (n)    -   If the new measurement Tmeas (n) is less than the previous value        T(n−1), then the filtered value at time (n) is reduced by a        small amount: T(n)=T(n−1)−(1−1)*[T(n−1)−Tmeas(n)] where 1 is a        parameter used for tuning noise rejection (this subtracts a        proportion of the difference between the two values from the        previous value).        In algorithmic form, this gives a non-linear (‘one way’) filter        algorithm as follows:        T(O) is initially set to the measured battery level during idle        mode        Begin measurement loop;

Do a voltage ADC (Analog to Digital Conversion);

Ti=New ADC Reading If T1 > T then T=T1 else T=T-(1-1)*(T-T1) Send valueof T to the battery display management for level comparison Wait 5seconds Repeat

By applying this filter to the plot shown above, this gives awaveform<T(n)> that ‘rides’ on top of the envelope of the measured ADCs,as shown in FIG. 2.

This level is compared against the existing discharge levels todetermine the battery capacity while in communication.

FIG. 3 is a block diagram of a portion of mobile phone 300, arranged tomeasure the level of battery 330 as described hereinabove. Mobile phone300 includes current source 320, which provides a charging current tobattery 330. Analog-to-digital converter (ADC) 340 measures the voltagelevel of battery 330. Filter 350 performs a filtering algorithm on themeasurements of ADC 340, as described above, to determine a valueindicative of the charge level of battery 330. Display 310 provides afour-segment display indicative of the charge level of battery 330.

1. A method of measuring the voltage level of a mobile telephone batteryduring a charging operation comprising the steps of: (a) applyingcurrent from a current source to charge the battery; (b) temporarilycausing the current from the current source to cease, to enable thebattery to enter a discharge mode; (c) measuring the voltage level ofthe battery when in the discharge mode; (d) re-applying current from thecurrent source; and (e) repeating steps (b) and (c) until the measuredvoltage exceeds one or more pre-determined voltage thresholds.
 2. Themethod of claim 1, wherein step (b) further comprises drawing a currentfrom the battery to rapidly place the battery into the discharge mode.3. The method of claim 2, wherein the current drawn from the battery isequivalent to operational drain.
 4. The method of claim 2, wherein thecurrent drawn from the battery is approximately 100 mA.
 5. The method ofclaim 1, wherein a first period over which the current from the currentsource is caused to cease is short in comparison to a second period overwhich the current from the current source is applied.
 6. The method ofclaim 5, wherein the first period is approximately one second and thesecond period is approximately nine seconds.
 7. The method of claim 5,wherein, for approximately two-thirds of the second period, the chargeis approximately 95% efficient.
 8. The method of claim 1, wherein abattery level display on the telephone indicates the charge level of thebattery in dependence on which the pre-determined voltage threshold orthresholds has or have been exceeded.
 9. The method of claim 8, whereinthe battery level display indicates four battery charge levels.
 10. Themethod of claim 9, further comprising only determining crossover of eachof the first three battery charge levels.
 11. The method of claim 1,further comprising: performing an analog to digital conversionmeasurement while applying the current from the current source to chargethe battery; and temporarily causing the current from the current sourceto cease only after the analog to digital conversion measurement isgreater than approximately 95% of a typical battery voltage.